1. Field of the Invention
This invention relates to a bearing seal for a universal ball joint primarily for use in aircraft pneumatic bleed air ducting.
2. Description of the Prior Art
In the prior art there have been universal ball joints that are interposed in pneumatic bleed air ducting such as aircraft pneumatic bleed air ducting. However, due to the contraction and expansion of the ducting and the construction of the joints, the coefficient of friction between the parts that allow angulation of the universal ball joint is extremely high resulting in a high joint bending moment.
When an aircraft jet engine is activated the bleed air passing through the engine port into the pneumatic bleed air ducting can reach temperatures up to 1250.degree. F. This of course causes thermal deflection of the ducting and thus one need for universal ball joints to be able to angulate and accommodate the deflection.
The universal ball joint with its angulation capabilities will also be able to be bent to compensate for installation tolerances during installation, aircraft structural deflections and vibration deflections.
When one ball joint is connected to another ball joint with or without a straight tube between the two ball joints and when this subassembly is connected to an elbow with a bend angle greater than 30.degree. and less than 150.degree. and when the elbow is connected to a third ball joint this forms a "three-bar-linkage." When ducting is connected to three ball joints such that two ball joints have their center line axes in line or approximately in line and this subassembly is attached to a third ball joint at an angle of at leat 30.degree. but no more than 150.degree. this also forms a "three-bar-linkage." A three-bar-linkage has the ability to have one end held fixed and provide X,Y,Z,.theta.x,.theta.y,.theta.z (motion at the other end while the three flexible joints only angulate.
One form of a prior art universal ball joint was a two piece joint where there was metal to metal contact so that as the joint was bent there was metal galling and an extremely high coefficient of friction.
Another form of a prior art attempt to conquer the coefficient of friction was to coat the contacting metal to metal parts the universal ball joint with various types of lubricants. While it is estimated that the initial coefficient of friction might be between 0.07 to 0.10, the more that type of universal ball joint was angulated the lubricant film would break down resulting again in metal to metal contact and a great increase in the coefficient of friction on the magnitude of 0.30 to 0.35 and greater.
Another form of prior art universal ball joint used ball bearings between the moving parts. However, such construction increased both the cost and weight of the joint because of the need for some form of retainer means for the ball bearings and the multiple bearings themselves.